1. Field of the Invention
The present invention relates to a process unit which includes a drum frame by which a photoconductor drum is supported and a development frame by which a development roller is supported.
2. Description of Related Art
A process unit which is removably installed in an image forming apparatus such as a printer is known in the art, for example, as disclosed in Japanese Laid-Open Patent Application, Publication No. JP 2007-127995 A.
The process unit disclosed in JP 2007-127995 A includes a photoconductor cartridge by which a photoconductor drum is rotatably supported and a development cartridge by which a development roller is rotatably supported, the development cartridge being attached to the photoconductor cartridge. A rotatory force produced in the image forming apparatus is transmitted to the development roller by a coupling joint (development coupling) provided at one end in a longitudinal direction of the development cartridge, thereby causing the development roller to rotate. In order that an outer peripheral surface of the development roller should have uniform surface contact with an outer peripheral surface of the photoconductor drum, the development cartridge is pressed against the photoconductor drum by a pressing mechanism.
In the meantime, when the development roller is caused to rotate by the rotatory force transmitted through the coupling joint, a torque about the axis of rotation of the coupling joint acts on the development cartridge. When the torque is small, it would not affect an image to be formed. However, as the torque of the development roller becomes larger due to increase in the image-forming (printing) speed, the torque acting on the development cartridge will become larger accordingly. Since the development cartridge is not fixed relative to the photoconductor drum, the rotatory driving force transmitted through the coupling joint causes the development cartridge to oscillate. As a result, the pressing force acting on the interface between the development roller and the photoconductor drum would become unstable at around the end of the development roller to which the rotatory force is transmitted from the coupling joint; therefore, the pressing force would disadvantageously become excessive, resulting in fogging (a blur or smudge in areas where no toner should have been applied), unevenness of density in proximity to a side edge of a sheet on which an image is formed, or other adverse effects on the quality of the image to be formed.
It would be desirable to form an image of good quality with a stable pressing force provided between the photoconductor drum and the development roller even if the torque acting on the development cartridge becomes larger. The present invention has been made in an attempt to address the above disadvantage. Illustrative, non-limiting embodiments of the present invention overcome the above disadvantage and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantage described above, and an illustrative, non-limiting embodiment of the present invention may not overcome any problem described above.